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Why is it that large generators cannot lack "excitation current"? Do you know the secret behind this?
Large generators play a key role in today's electrical power systems. Whether in power plants or other power supply facilities, the operation of these generators depends on a key element called "excitation current". The establishment of the excitation current is crucial for the proper operation of the generator, but why is this so? This article will take a closer look at the importance of excitation current and the technical principles behind it.
Magnetic excitation is the process of generating a magnetic field through electric current and is fundamental to the proper functioning of any generator.
Basic principles of excitation
The field current is the current used to create the magnetic field inside the generator. In most large generators this is usually accomplished by means of electric field coils. These electric field coils require current to flow through them to generate a magnetic field that can rotate. Without current flowing through these coils, the generator will not be able to convert energy efficiently, which will affect the stability of the entire power system.
A generator without excitation current produces almost zero voltage, which makes it impossible to start the power generation process.
Self-excitation and external excitation
In larger or older generators, a separate excitation device is often used to generate the excitation current. This device is usually a small permanent magnet or battery powered generator designed to provide the required excitation current for the main generator. However, many modern generators are self-excited, meaning that their components are able to use part of their own output to continuously power the field coils.
The self-excited motor gradually builds up a strong electric field through a feedback process, ultimately generating the required voltage.
Key Challenges of the Startup Process
For self-excited motors, starting must be done without external load. If an external load is connected, the generator's energy will be rapidly consumed and insufficient voltage will be created to gradually increase the output. Furthermore, to avoid problems during startup, many devices are designed with a “flash field” feature to ensure that current can be injected in the absence of sufficient residual magnetism.
Flash field is a method of briefly injecting current to achieve excitation, and many small generators may also require this function during starting.
The rise of brushless excitation technology
With the advancement of technology, brushless excitation technology has gradually replaced carbon brush excitation, reducing the need for daily maintenance and reducing the fire risk associated with carbon brushes. This technology is mainly based on the design of a rotating diode rectifier, which can effectively extract energy from the induced alternating voltage to provide current for the field winding of the generator.
ConclusionAlthough brushless excitation technology has some limitations in terms of fast falling magnetic fields, the situation has improved with the emergence of new solutions.
In summary, the operation of large generators is inseparable from the excitation current, which is not only the basis of power production, but also the key to the stability of the entire power supply system. Understanding how it works can help us better understand and apply these technologies, ensuring that the systems can operate efficiently and stably amid the growing demand for electricity. With the continuous innovation of science and technology, how will the excitation technology develop in the future?
